We propose to continue research upon the structure, genetics, and mode of replication and assembly of bacteriophage 0X174. Methods have been developed for the degradation of the viral DNA into specific, genetically characterized pieces. The application of such methods to the analysis of intermediates in viral replication and assembly is yielding new information as to their structure. We hope to undertake in vitro and quasi-in vitro studies of 0X replication, transcription, and translation to permit better resolution of these processes.